Biden raised his right hand and took his oath of office Tuesday from Associate Justice John Paul Stevens. In that moment, he became second-in-command to both Barack Obama and to a nation eager for change.
The swearing-in came shortly before Obama was to take his own oath on the West Front of the Capitol.
The vice president's most vital role is to assume the presidency in the event Obama cannot serve. Beyond that, his duties can be limited or expansive based on the wishes of his boss, the president.
Biden says he plans to loyally support Obama but also wants an active role in decision-making.
The 66-year-old Biden served 36 years as a Delaware senator.